I built http://www.bitpixels.com http://www.bitpixels.com a while ago, when I needed to generate thumbnail images and the available options were too expensive.

I built http://www.bitpixels.com http://www.bitpixels.com a while ago, when I needed to generate thumbnail images and the available options were too expensive. It's available for free and serves a few million thumbnails a month. I didn't add a lot of advanced features (it's a side project), but it's stable and gets the job done.